Double Difference Ambiguity Resolution for GLONASS/GPS Carrier Phase

The satellite constellation and the signal structure of the Russian GLONASS and the US GPS are comparable. GLONASS observations can be processed similarly to GPS data, if the differences in the reference frame, the system time and in the frequencies of the satellite signals are taken into consideration. The last item leads to a new term in the double difference phase observation equation and may destroy the integer nature of the ambiguities. This new term depends on the wavelength difference of the two satellites involved and the error in the initial sin-gle difference ambiguities. In order to account for the new term, we use an iterative ambiguity resolution algo-rithm and solve for one double difference ambiguity in each iteration step. In the first iteration step the ambiguity with the smallest rms error, resp. the smallest wavelength difference of the two satellites, will be fixed to an integer number if certain criteria are fulfilled. Each successfully resolved double difference ambiguity of a satellite pair with different wavelengths leads to an improved accuracy of the single difference ambiguities in the next iteration step. Thus, the new term is getting smaller with each it-eration step and this should finally allow to resolve the double difference ambiguities for all satellite pairs. The algorithm is mainly suited for static GLONASS/GPS processing of long sessions ( ³ 1 hour). We show the re-sults of the ambiguity resolution of two baselines having a length of 5 m and 6.6 km, respectively.